Sludge dewatering apparatus

ABSTRACT

An apparatus for removing aqueous liquid having a lower content of solids, if any, from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to obtain a product having a higher solids content, has two endless, driven belts of elongated porous sheets. The belts are supported so that one belt has its path of travel inside that of the other belt. The outer belt is supported so that it has an upper horizontal run through three zones. The inner belt is moved in the same direction and has upper horizontal runs through the first and third of those zones. At the intermediate zone the belt moves downwardly and then upwardly. The outer belt overlies and abuts the inner belt at the first and third zones and is spaced from it at the intermediate zone. The sheet of the inner belt is resilient, compressible and made of cellular material capable of absorbing an aqueous liquid by a wicking action, whereas the sheet of the outer belt is a fine-mesh sheet with pores providing passage of the liquid through the sheet by the wicking action of the abutting cellular sheet of the inner belt while most of the solids are retained on the outer belt. A feeder for delivering flowable material on to the outer belt is mounted adjacent the beginning of the first zone. At the intermediate zone a pair of opposed rolls compress the inner belt to remove aqueous liquid. The inner belt is a composite assembly of the sheet of cellular material, a backing sheet and overlying strands secured to the backing sheet at widely spaced locations to avoid affecting substantially the planarity of the outer surface of the sheet of cellular material.

United States atent Levin et a1.

[54] 'SLUDGE DEWATERING APPARATUS [72] Inventors: Paul Levin, Morton Grove; Maximilian Adamski, Wheeling, both of Ill.

[73] Assignee: General American Transportation Corporation 22 Filed: July 26, 1971 21 Appl.No.: 166,086

[52] US. Cl. ..l00/l18, 34/70, 100/112, 100/152, 210/386, 210/499 [51] Int. Cl. ..B30b 9/24 [58] Field ofSearch ..100/1l2, 118,117, 116,122, 100/151-154, 37; 210/351, 386, 387, 388, 401, 499; 34/14, 70, 71,152

[56] References Cited UNITED STATES PATENTS.

1,778,342 10/1930 Thompson ..l00/l 18 X 1,958,279 5/1934 Morgan ..l00/l18 X 2,207,278 7/ 1940 Albrecht .l00/l 18 UX 2,756,668 7/1956 Seed et a1. 100/1 18 X 3,315,370 4/1967 Hikosaka ..34/70 FOREIGN PATENTS OR APPLICATIONS 760,226 6/ 1967 Canada 100/ l 18 Primary Examiner-Billy J. Wilhite Att0rneyClaron N. White 5 7] ABSTRACT An apparatus for removing aqueous liquid having a [151 3,699,881 51 Oct. 24, 1972 lower content of solids, it any, from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to obtain a product having a higher solids content, has two endless, driven belts of elongated porous sheets. The belts are supported so that one belt has its path of travel inside that of the other belt. The outer belt is supported so that it has an upper horizontal run through three zones. The inner belt is moved in the same direction and has upper horizontal runs through the first and third of those zones. At the intermediate zone the belt moves downwardly and then upwardly. The outer belt overlies and abuts the inner belt at the first and third zones and is spaced from it at the intermediate zone. The sheet of the inner belt is resilient, compressible and made of cellular material capable of absorbing an aqueous liquid by a wicking action, whereas the sheet of the outer belt is a fine-mesh sheet with pores providing passage of the liquid through the sheet by the wicking action of the abutting cellular sheet of the inner belt while most of the solids are retained on the outer belt. A feeder for delivering flowable material on to the outer belt is mounted adjacent the beginning of the first zone. At the intermediate zone a pair of opposed rolls compress the inner belt to remove aqueous liquid. The inner belt is a composite assembly of the sheet of cellular material, a backing sheet and overlying strands secured to the backing sheet at widely spaced locations to avoid affecting substantially the planarity of the outer surface of the sheet of cellular material.

16 Claims, 13 Drawing Figures 8/ SECOND 5mm: Q77 0 77 i i coMPREsswN l WASH\ DRIVE W68 y Q 7 ROLLS s1 (9- )62 T612 0 .20 52 g e5 66 31 C) M INITIAL PARTIAL FIRSTCOMPRES SECONDARY/MR TIAL DEWATEIZ- DEWATERING- ZONE 510M ZONE V 22 f@ o 0 0 a \e, 2;

Re "5'4- 87 CAKE REMOVAL PATENTED 0m 24 I972 SHEEI 1 [IF 3 PARTIAL DEWATERING zone INVENTORS M Paul LCI/fZ/ankd azimil 'an am: 1.

CROSS REFERENCE TO RELATED APPLICATIONS This invention is related in subject matter to application SerfNo. 773,204 issued as U.S. Pat. No. 3,601,039

' on Aug. 24, 1971 and application Ser. No. 849,770 issued as U.S. Pat. No. 3,613,564 on Oct. 19, 1971.

The second of those patent applications discloses and claims an apparatus that is an improvement of the apparatus disclosed and claimed in the first application. The present application is further improvement of the sludge dewatering apparatus of the invention of the first patent application. Like the improvement of the apparatus of the second patent application the apparatus of the present invention has two endless belts moving in the same direction .with horizontal runs at which the outer belt overlies and abuts the inner belt for a partial dewatering of flowable material fed to the outer belt. Downstream of the partial dewatering zone, the upper horizontal runs of the two belts in abutment with each other can be subjected to a compressive force for further dewatering of the material on the outer belt at a compression zone at which a second set of belts overlie the first set. At this compression zone the belts of the second set, inabutting relationship for their lower horizontal run, pass in the same direction with the belts of the first set between pairs of opposed rolls to apply a number of compressions, with intermediate expansions, of the cellular sheet of the inner belt of the first set and the inner belt of the second set. That inner belt of the second set has a resilient, compressible sheet made of cellular material that is preferably capable of absorbing aqueous liquid by a wicking action.

The inner belt of the first set of belts in the apparatus of the second patent application is preferably a composite assembly that includes the sheet of porous, resilient, compressible sheet made of cellular material and a backing sheet that is an elongated sheet of coarse mesh adhered to the adjacent surface of the sheet of porous cellular material, whereby the composite sheet as an endless belt has sufficient strength to prevent breaking under tension imparted to the belt during use of the apparatus. Such tension can be sufficiently high to cause breaking of the sheet of porous cellular material when used alone as an endless belt.

One improvement of the apparatus of the present invention over the apparatus of the second patent application is the separation of two portions of the partial dewatering zone into two zones by an intermediate zone at which the inner belt is spaced from the upper horizontal run of the outer belt. At this intermediate zone the apparatus includes means to compress the separated inner belt for removal of aqueous liquid received by that belt through the pores of the outer belt as a result of the wicking action in the first portion of the dewatering zone.

Another improvement of the apparatus of the present invention is the nature of the composite assembly of the sheet of the inner belt. The new composite assembly prevents breaking of the belt under tension and minimizes the tearing or gouging out of portions of the sheet of porous cellular material from the outer surface of that sheet. The belt of this composite assembly has a longer life expectancy without substantial impairment of dewatering efficiency.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an apparatus for removing water or other liquid from flowable materials containing such water or liquid as the continuous phase and suspended solids as a discontinuous phase.

The field of the invention is best illustrated by one use, viz., the use of the apparatus for the dewatering of sludge from sewage by which use aqueous liquid is removed so that the material remaining has a higher solids content. This illustration of the field of use is presented in some detail in the second patent application.

2. Description of the Prior Art The most pertinent prior art is the apparatus of said two copending patent applications. The nature and solids content of sludges from sewage treatment are presented in detail in those copending applications that are hereby incorporated by reference.

SUMMARY OF .T HE INVENTION The apparatus of the invention comprises: a first endless belt; means to support said belt at various positions; means to move said endless belt through a path of travel including an upper run through three zones; at second endless belt; means to support said second endless belt at various positions; means to move said second belt through a path of travel including an upper run through said three zones; means mounted above said second belt' to deliver flowable material to said second belt upstream of the three zones; means mounted to remove product of lower liquid content and thus product of high solids content from said second endless .belt downstream of 'the three zones; means at the second zone, as a first compression zone, to compress the sheet of porous cellular material of the first belt while spaced from the second belt; means downstream of the third zone at a second compression zone to compress said sheet of porouscellular material of said first belt; means located at the first compression zone to collect aqueous liquid removed from said sheet of porous cellular material; and means located at the second compression zone to collect aqueous liquid removed from and moving downwardly from that sheet. The first and third zones, between which is located the second zone, i.e., the first compression zone, are initial and secondary partial dewatering zones at which the second belt overlies and abuts the first belt.

The first endless belt is supported and moved by the supporting means and the moving means so that at any given time a portion of the belt is at a lower run and another portion is at an upper run. The supporting means for the first belt is constructed such that the upper run of the first belt passes through the first, second and third zones. The first belt includes an elongated, compressible and resilient sheet of a porous cellular material capable of absorbing said aqueous liquid by a wicking action. Through the first and third zones the outer surface of that elongated sheet is at a horizontal plane whereas through the second zone that outer surface is below that horizontal plane.

The second belt includes an elongated different porous sheet, said different porous sheet being a finemesh sheet with pores extending through the sheet and of a size within a predetermined range for passage of said aqueous liquid of the continuous phase of said flowable material through said pores, from the outer surface to the inner surface of said different sheet, by a wicking action of said cellular sheet when it is in abutment with said inner surface of said different sheet, and for retention at the same time on said outer surface of said different porous sheet of a major portion of the suspended solids of said fiowable material to obtain at least a partial removal of said aqueous liquid from said flowable material.

The supporting means for the second belt is such that a portion of the belt as an upper run, at which the outer surface of said different porous sheet faces upwardly, passing horizontally through said first, second and third zones so that the inner surface of said different porous sheet is in abutment with the outer surface of said elongated sheet of porous cellular material for said wicking action at said first and third zones, as initial and secondary partial dewatering zones, and is spaced from the outer surface of said elongated sheet of porous cellular material at said second zone, as the first compression zone, and to provide another portion of said second belt as a lower run. The moving means for the second belt moves it"so that its upper run through the first and third zones is in the same direction as the movement of the upper run of the first belt.

Because the supporting means for the second belt supports that belt through the first, second and third zones of its upper run in a horizontal direction the different porous sheet is in abutment with the outer surface of the elongated sheet of porous material at the initial and secondary partial dewatering zones, whereas the inner surface of that different porous sheet is spaced from the outer surface of the elongated sheet of porous cellular material of the first belt at the second zone, i.e., the first compression zone. Thus at the first and third zones the abutment of the different porous sheet with the elongated sheet of porous cellular material makes possible the wicking action for removal of aqueous liquid from the flowable material fed to the delivery means mounted above the second belt at a location adjacent the beginning of the first zone, that is the initial partial dewatering zone. Due to the spacing of the two belts at the second zone the compression means provides opposed forces on the elongated sheet of porous cellular material to remove aqueous liquid from that sheet of the first belt without applying the opposed forces to the then spaced second belt and, of course, without applying the opposed forces to the partially dewatered flowable material on the second belt. In the third zone where the two belts again are in abutment with each other further wicking action occurs for an additional removal of aqueous liquid from the material on the second belt by the first belt so that the third zone is the secondary partial dewatering zone.

Means to remove product of lower liquid content from the second endless belt is located downstream of the secondary partial dewatering zone. The second compression zone can be located upstream or downstream of the means to remove product of lower liquid content. When it is located downstream of that product removal means, the second compression means at the secondicompression zone is located such that the two belts have been spaced from each other in a continuation of their paths of travel. in that case the product removal means is also located to effectuate product removal from the second belt while it is spaced from the first belt in their paths of travel. Alternatively, when the second compression zone is located upstream of the means for removal of product from the second belt, the compression means in that zone is located at the upper run of the two belts downstream of the secondary partial dewatering zone but while the two belts are in abutment with each other, whereas preferably the product removal means is located beyond the travel where the two belts as an upper run of each are in abutment with each other. As seen later, for some materials to be partially dewatered it is feasible to remove sufficient aqueous liquid by the first alternative in which the second compression zone is located to provide opposed forces on the first belt not while the belts are together but at the lower run of the first belt where it is spaced from the second belt at its lower run.

in the apparatus of the present invention means located at the first compression zone to collect aqueous liquid is positioned relative to the compression means at that zone so that it collects the removed aqueous liquid that is moving downwardly from the sheet of porous cellular material of the first belt. Similarly, liquid collection means mounted downstream of the third zone to collect aqueous liquid is located at the second compression zone to collect aqueous liquid removed by the second compression means and moving downwardly from the sheet of porous cellular material of the first belt.

The first endless belt is a composite assembly that includes the elongated, compressible and resilient sheet of the porous cellular material stated above. Examples of such porous cellular material are fine-pore cellulose sponge and cellulosic foam in sheet form. This sheet of cellular material is water absorbent and by a wicking action aqueous liquid is transferred from one cell to another so that the entire sheet can absorb and retain until compressed an amount of water that is many times the weight of the cellular material. It is preferred that the cell size be sufficiently small to prevent downward passage of a substantial amount of suspended solids in the aqueous liquid from the top surface portion of the sheet. This minimizes internal clogging of the sheet by solids, but this requirement for small size is mitigated by the choice of the different porous sheet of the second endless belt. Of course, this porous sheet of the first belt is required to be flexible so that the sheet of material can be bent as it goes around rolls at the ends of the upper run. As a result, the sheet is kept in damp form between uses of the belt to maintain the requisite degree of flexibility. The sheet of porous cellular material is relatively thick, e.g., one-half inch.

The composite assembly of the first belt further includes a backing sheet that has wide pores or openings so that the backing sheet has a minimum amount of material in the path of travel of aqueous liquid forced out of the sheet of porous cellular material when the latter sheet is compressed. At the same time the construction of the backing sheet must be such that it has sufficient strength as an endless belt to withstand the tensile forces occuring when the belt is driven in its path of travel during its use in the apparatus. An endless backing sheet meeting these requirements is made from a coarse-mesh screen or sheet of extruded polypropylene that has sufficiently large diameter extruded filaments extending longitudinally and transversely to provide adequate strength for use as an endless belt and yet has the desired large openings mentioned above. Such sheet is commercially available and is made by an extrusion operation to provide warp strands and woof strands joined to one another at their intersections. Of course, the backing sheet, like the sheet of porous cellular material when damp, is flexible. Thus the composite assembly of the first belt is sufficiently flexible to bend around a driven roll and a number of other rolls mounted in a manner to provide the support for the first belt in its path of travel.

This composite assembly of the first belt includes elongated, relatively narrow sheets of flexible material secured to the longitudinal margins of the backing sheet and having external longitudinal margins that are beaded to be engaged by tracking devices that are disposed along the path of travel of each edge of the composite assembly at various locations to maintain alignment of the belt in its path of travel.

The foregoing construction of the composite assembly of the first belt is the same as that disclosed in said second copending patent application in which it is disclosed that the sheet of porous cellular material is adhered at its inner surface to the backing sheet. In the preferred aspect of the apparatus of the present invention the sheet of porous cellular material is not adhered to the backing sheet by glue or other adhesive. Instead it is secured to the backing sheet by the presence of a number of strands of material that extend longitudinally along the outer surface of the sheet of porous cellular material, that are spaced from one another, and that are connected through the sheet of porous cellular material .to the backing sheet at substantially spaced intervals. In addition to the longitudinal strands thus secured, the composite assembly preferably includes transverse strands that intersect the longitudinal strands. The longitudinal and transverse strands are secured to the backing sheet at those intersections. In this preferred construction, the longitudinal strands and the transverse strands are provided by a wide-mesh flexible sheet made of metal or a plastic such as polypropylene. The strands have or the wide-open mesh sheet having such strands has a strength sufficient to preclude the breaking of the strands during the use of the composite assembly as the first belt. Thus the strands cooperate with the backing sheet to provide the requisite tensile strength to avoid breaking of the belt.

The foregoing construction of the assembly of the first belt protects the sheet of porous cellular material to a substantial degree against loss of portions of the porous cellular material from relatively large areas of the composite belt. In the absence of such secured strands, such loss is a problem at the juncture of ends of slabs of porous cellular material when slabs are used to make the first endless belt. Additional loss of this type in the body of a slab due to flexing action around rolls or by a gouging action occurring with the water sprayin g in the cleaning zone for the belt is minimized by the presence of the strands secured to the backing sheet. Because this preferred composite assembly minimizes tearing of the sheet of porous cellular material, the useful life of the belt is very substantially lengthened. Whenever a portion of a slab of the sheet of porous cellular material is fractured during use,'the line of the tear is often precluded from extending itself because the-overlying secured strands at that region preclude substantial relative movement of the adjacent portions of the sheet of porous-cellular material.

In this preferred embodiment of the composite assembly it is not necessary to glue the sheet of porous cellular material to the backing sheet. The strands, by being secured to that backing sheet, serve this function. These strands on the outer surface of the sheet of porous cellular material, that must be abutted by the different porous sheet of the second belt for water removal by the wicking action, have a width and spacing relative to each other such that they overlie only a minor portion of the area of the outer surface of the sheet of porous cellular material. Those dimensions and the manner of securing the strands to the backing sheet must be such that a major portion of the outer surface of the sheet of porous cellular material remains flat at the horizontal part of the upper run where the different porous sheet of the second belt should be in intimate contact with a sufficient area of the outer surface of the sheet of porous cellular material. This is at the first and second partial dewatering zonesof the apparatus. This retained area of flatness of the outer surface of the sheet of porous cellular material of the preferred embodiment of the composite assembly of the first belt should be at least percent for the apparatus to be considered economic at the present cost of materials and of construction. It is preferred that this area be at least percent and it is especially preferred that it be percent.

Whereas the backing sheet of the composite assembly of the first belt has pores of adequate size to minimize hindrance to flow of water from the sheet of porous cellular material when it is compressed, the pores of the backing sheet are rather small in size when compared with the spacing between the strands secured to the backing sheet and mounted on the outer side of the sheet of porous cellular material. For example, the backing sheet may have 16 pores per lineal inch, whereas the strands are spaced so that they are illustratively about 3 to 4 inches apart.

The second endless belt includes the elongated different porous sheet having the characteristics stated above. Of course, that sheet is flexible and it is thin relative to the sheet of porous cellular material. Preferred materials for that sheet are polypropylene, high-density polyethylene and polyester. When the sheet is made of polyester, the sheet can be a polyester monofilament plain weave cloth such as described in said second copending patent application. Such cloth is available in different sizes of mesh openings ranging from 53 microns to 840 microns. The 53-micron cloth has a 275 mesh count per inch and has a 32 percent open area. This sheet when using other material, such as polypropylene and polyethylene mentioned above, has such mesh size and percent of open area.

The specific different porous sheet that is used is dependent upon the nature of the flowable material to be dewatered. The nature of the fiowable material can be affected desirably by the addition of material such as polymers to the flowable material, such as sludge, to provide sufficient coagulation of solids in the flowable material.

. This different porous sheet of the second belt is not limited to the use of a belt made of organic material. It can be made of a metal mesh cloth. Although the material of the sheet is preferably one that is essentially hydrophobic for ease of removal of dewatered product, the sheet can be made of a material that is hydrophilic.

In one-embodiment of the apparatus of the invention the second compression means at the second compression zone includes a number of additional rolls, above the two belts and the lower run of a second set of belts second zone is also a partial dewatering zone and is not a compression zone in which the sheet of porous cellular material of the first belt is compressed while it is spaced from the second sheet. In these other embodiments the support means for the first belt supports the first belt at the second zone so that the top surface of the sheet of porous cellular material is also at the horizontal plane of that surface in the first and third zones. Thus, in effect, there is one partial dewatering zone of a length corresponding to the three zones of the upper run of the unmodified apparatus. .That partial dewatering zone corresponds to the wicking zone shown in FIG. 2 of said second copending patent application.

that are above the first and second belts. The two sets of belts pass between these additional rolls and opposed rolls that provide part of the support means for the first and second belts at a portion of their horizontal run downstream of the secondary partial dewatering zone. This construction corresponds with the compression zone and means of the apparatus disclosed in said second copending patent application. As in that apparatus the second set of belts comprises a first belt including a sheet of porous cellular material and a second belt including a different porous sheet. Those two belts of the second set correspond in their nature with the first and second belts mentioned above except that the first belt of the second set is not required to be capable of absorbing aqueous liquid by a wicking action. Thus other materials can be used as the sheet of porous cellular material of the first belt of the second set of belts than specified for the sheet of porous cellular material.

of the first belt of the first set of belts. The material may be polyurethane of the porous cellular type.

In the embodiment of the apparatus of the invention in which the additional rolls and the second set of belts are not present above the first set of belts at the second compression zone, the apparatus utilizes an opposed pair of rolls at a zone downstream of the upp'er run of the first belt to provide a second compression of that belt. Such pair of opposed rolls can be part of the device used to wash the first belt. In that case the washing device removes aqueous liquid removed from the material by the wicking action at the secondary partial dewate ring zone and removes solids from the outer surface portion of the sheet of porous cellular material. In the washing station that outer surface of that sheet faces downwardly. This is not to say that the opposed rolls at a similar washing station in the embodiment of the apparatus using the additional rolls and extra set of belts does not remove some aqueous liquid; however, in that case the major portion of removed aqueous liquid received by the first belt at the secondary partial dewatering zone is removed from the first belt with additional aqueous liquid removed from the material by the number of compressions and expansions of the sheet of porous cellular material effected by the additional rolls and the opposed rolls at the second compression zone.

Two other embodiments of the apparatus of .the present invention are modifications of the two alternative embodiments described above. In each of these two other embodiments of the apparatus the first and third zones remain as partial dewatering zones, and the In both of these other embodiments of the apparatus it is required that the composite assembly of the first belt be constructed as described above rather than being constructed as disclosed in said second copending patent application. This is because the construction of that composite assembly affords the sole improvement of these embodiments over the apparatus of said second copending patent application. This composite assembly is not required for the alternative embodiments described earlier but is a preferred construction for the first belt of those embodiments. This composite assembly provides an additional improvement of the apparatus of those embodiments over the apparatus of said second copending patent application.

DESCRIPTION OF THE DRAWINGS The apparatus of the invention is illustrated by preferred embodiments in the accompanying drawings in which components that are the same and that provide the same function are generally designated by the same numeral and in which:

FIG. 1 is a fragmentary front elevational view, generally schematic, of one embodiment of the ap paratus of the present invention showing the use of the improved composite assembly of the first belt as the modification of the apparatus of said second copending application and thus lacking an initial compression zone between two partial dewatering zones;

FIG. 2 is a fragmentary perspective view of the upper run of the two main belts and showing them as they would appear when taken along line 29-2 of FIG. 1,

with portions of these two belts cut back different amounts and with the upper composite assembly of the second belt being turned up to show more clearly the construction of these two belts;

FIG. 3 is an enlarged fragmentary perspective view of the first belt showing only the outer surface of the sheet of porous cellular material, the wide-mesh sheet, and the top of fasteners securing the latter to the backing sheet;

FIG. 4 is an enlarged fragmentary perspective view, like FIG. 3, with a portion broken away to show the backing sheet and the entire configuration of one fastener;

FIG. 5 is an enlarged fragmentary perspective view of that composite assembly of the first belt in the inverted position that it has when it is at its lower run;

FIG. 6 is a fragmentary cross section of that composite assembly of the first sheet taken along' a line at which one of the fasteners is located;

FIGS. 7 through 10 are fragmentary cross sections like FIG. 6 but showing different means for securing the wide-mesh sheet to the backing sheet with the sheet of porous cellular material secured between these two sheets, with FIG. 8 showing two of these alternative constructions;

FIG. 11 is a front elevational view, generally schematic, of one especially preferred embodiment of the present apparatus;

FIG. 12 is an enlarged fragmentary view of a portion of the apparatus of FIG. 1 1; and

FIG. 13 is a front elevational view, generally schematic, of another especially preferred embodiment of the apparatus of the present invention.

DETAILED DESCRIPTION Referring to FIG. 11, which shows one of the especially preferred embodiments of the apparatus of the present invention in its use for the dewatering of sludge as the flowable material, the apparatus includes a lower set of two endless belts, one of which is a first belt generally indicated at 15 and the other being a second belt generally indicated at 16. The apparatus has an upper set of two endless belts. The first belt of the upper set is generally indicated at 17 and the second belt of the upper set is generally indicated at 18. The

belts 15 and 16 are composite assemblies of sheets.

Those composite assemblies have the construction described below and shown in FIGS. 3 through 6 or one of the modifications shown in FIGS. 7 through 10. Of course, the composite assembly of belt 17 includes a sheet of porous cellular material that is not required to be capable of absorbing aqueous liquid by a wicking action as is the case for the sheet of porous cellular material of the composite assembly constituting belt 15.

The apparatus further includes support rolls 20 between a driving roll 21 and a roll 22. The top surface of rolls 20, 21 and 22 are at the same horizontal plane to provide support for part of the upper run that is mostly horizontal for belt 15 and is horizontal for belt 16. A set of rolls 23 is also mounted so that their top surfaces are at this horizontal plane. The set of rolls 23 are between support rolls 20 and roll 21. The rolls 23 provide support of belts 15 and 16 at another part of their upper run that is horizontal. The apparatus has an upper roll 24 and a lower roll 25 that are opposed to each other, and both are below the horizontal plane mentioned above. The rolls 24 and 25 are between two sets of rolls 20. The belt 15 is passed between rolls 24 and 25 and is otherwise supported at its upper run by rolls 20, 21, 22 and 23. The belt 16 is not passed between rolls 24 and 25 and thus extends horizontally between the two sets of rolls 20 at an elevation above roll 24. With this construction there are three zones for the upper run of belts 15 and 16 from roll 22 to rolls 23. Legends have been added to FIG. 11 to indicate the function of these three zones. In the first zone, that is the zone closest to roll 22, both belts are supported by the one set of rolls 20 with belt 16 overlying and in abutment with belt 15. That zone is designated as initial partial dewatering zone. In the next zone belt 15 is diverted downwardly from and then upwardly back to its horizontal run in the first and third zones by being trained around the bottom of roll 24, which cooperates with opposed roll 25 to compress belt 15. Through that zone, called the first compression zone, while belt 15 is l 0 spaced below belt 16, belt 16 continues its horizontal travel to the third zone, that is called the secondary partial dewatering zone. The second set of rolls 20 support both belts in the third zone for a horizontal run with belt 16 overlying and abutting belt 15.

The apparatus has a delivery tube 30 connected to a manifold pipe 31 having downwardly facing openings through which sludge flows on to belt 16 adjacent the beginning of the upper horizontal run of belt 16 through the initial partial dewatering zone. The sludge is fed to pipe 30 from a source not shown. The manifold pipe 31 feeds the sludge to belt 16 across a substantial part of the effective width of that belt.

The apparatus has a set of rolls 33 that are mounted to be opposed to rolls 23 so as to provide adjustable opposed forces on belts l5 and 16 supported by rolls 23 and on belts 17 and 18, at a lower portion of their lower run, also passing between the opposed sets of rolls 23 and 33. The belt 15 is supported and/or guided in its lower run from roll 21 to roll 22 by rolls 34. During its lower run belt 15 passes between two sets of upper rolls 35 and lower rolls 36 that are mounted to compress belt 15 as it passes between eachpair of rolls 35 and 36. Adjacent rolls 35 and 36 and between those rolls and roll 21 there is located, below belt 15, a manifold pipe 37 having upwardly facing holes to feed wash water under pressure from manifold pipe 37 that is connected to a water source not shown. By this construction aqueous liquid remaining in belt 15 after leaving the last pair of opposed rolls 23 and 33 is rinsed from belt 15 along with any solids on the outer surface of belt 15. By this construction any remaining aqueous liquid is substantially removed with rinse water as belt 15 passes between the opposed sets of rolls 35 and 36. Thus rolls 35 and 36 are at another compression zone. Below opposed sets of rolls 35 and 36 and manifold pipe 37 is mounted a liquid collection pan 40 that receives wash water, and aqueous liquid and solids removed from belt 15 resulting from the use of wash water from manifold pipe 37 and compressions provided by the opposed sets of rolls 35 and 36. At this compression zone belt 16 is not present because the lower run of belt 16 is below and spaced from belt 15, roll 37 and pan 40. The belt 16 is trained around a roll 41 adjacent but at a lower elevation than roll 21. A scraper blade 42 removes partially dewatered product from the outer surface of belt 16 before it leaves roll 41 to begin its lower run.

A liquid collection pan 43 is located below rolls 24 and 25 at the first compression zone to receive and collect aqueous liquid squeezed out of belt 15 as it passes between rolls 24 and 25 at that zone.

A liquid collection pan 44 is mounted below rolls 23 to receive aqueous liquid forced out of belt 15 by its -compression as it passes with belts 16 through 18 tial part of the periphery of the roll 22 from which starts the upper run of both belts.

Between rolls 41 and 50 belt 16 is supported by rolls 51. The belt 15 passes over an adjustable tension roll 52. Some of the rolls 51 are located so that between two of them, by the presence above of another roll 53, belt 16 has a downwardly inclined path of travel as part of its lower run. During that inclined path of travel belt 16 is washed by rinse water from a manifold pipe 54 below. The pipe 54 is connected to a water source not shown. A liquid collection pan 55 is placed below this inclined path of travel of belt 16 to receive rinse water and solids not previously removed by scraper blade 42.

The first belt 17 of the upper set of belts is trained about a driving roll 60 and a roll 61 between which there is an upper run and a lower run of belt 17. The belt 17 is supported by a set of rolls 62 at a higher horizontal portionof the upper run and by another set of rolls 62 at a lower horizontal portion of the upper run and by another set of rolls 62 at a lower horizontal portion of the upper run. There is another portion of the upper run between these portions. In that another portion belt 17 passes downwardly under a roll 64, then between a lower set of rolls 65 and an upper opposed set of rolls 66 mounted to compress belt 17 passing between them and then upwardly to the higher horizontal portion of the upper run. The belt 17 between roll 60 and the lower horizontal portion of its upper run passes under a tension roll 66. A manifold pipe 68 having openings to direct rinse water onto belt 17 is adjacent but upstream of the compression afforded by rolls 65 and 66. The manifold pipe 68 is connected to a rinse water source not shown. At this washing zone where belt 17 is subjected to rinse water and before its compression by rolls 65 and 66 there is a liquid collection pan 69 to receive aqueous liquid rinsed from belt 17 and rinse water both squeezed from belt 17 by rolls 65 and 66.

The upstream end of the lower run of belts 17 and 18 is supported between rolls 61'and 60 by a set of'rolls 70 and a lower roll 71 to be spaced substantially above belts l and 16. The belts 17 and 18 pass under a roll 72 in a downwardly inclined path to gradually overlay belts l5 and 16 and then pass between rolls 23 and rolls 33 at the first compression zone with belts and 16. Beyond the first compression zone belts 17 and 18 are upwardly inclined to separate them from belts 15 and 16 moving to roll 21. This upward inclined travel is afforded by roll 60 having its bottom surface substantially above that of rolls 33.

The upper run of belt 18 is spaced above the upper run of belt 17 by being trained around a roll .75 above roll 61 and a roll 76 to the right (as viewed in FIG. 11) of roll 60. The upper run of belts 18 has a final horizontal portion provided by a set of support rolls 7'7 and an initial generally upwardly inclined portion at which it is supported by rolls 78 and 79, upstream of which it passes under a tension roll 80 adjustably mounted and adjacent roll 76 Roll 81 is above belt 18 and downstream of roll 78. Rolls 78 and 81 provide a generally horizontal portion of the run that isa washing zone. A manifold pipe 82 above belt 18 at this washing zone has downwardly facing openings through which wash water is fed to belt 18. The wash liquid is collected at this zone below belt 18 by a liquid collection pan 83. Very little, if any, of the washed liquid passes through belt 18, in view of its nature like belt 16, but

12 the wash liquid flows over the sides of the belt to be collected by pan 83.

Because belt 17 is trained around roll 60, whereas belt 18 is trained around roll 76, belts l7 and 18 separate at roll 60. The belt 18 is scraped by a scraper blade 85 like scraper blade 42. A collection pan 86 is below rolls 41 and 76 and scraper blades 42 and 85 to receive sludge cake removed from belts l6 and 18. The major portion of the sludge cake comes from belt 16.

The driving rolls 21 and 60 are driven by belts 87 and 88, respectively, engaging pulleys (not numbered) fixed on the shafts (not numbered) on which rolls 21 and 60 are mounted.

Referring to FIG. 13, which shows another of the especially preferred embodiments of the apparatus of the invention in such use, the apparatus differs from that shown in FIG. 11 in a number of respects. The important difference is the absence of the upper set of belts, the associated rolls to carry those belts through their paths of travel, rolls 33.that cooperate in the apparatus of FIG. 11 with rolls 23, scraper blade 85 and the wash devices for these belts.

In the apparatus of FIG. 13 rolls 23 are designated as rolls 20 because there is no compression zon'e having rolls 33. It is seen that the apparatus still has three zones at the upper run of belts 15 and 16. The secondary partial dewatering zone is longer clue to the absence of rolls 33 used for the second compression zone in the apparatus of FIG. 11. In this apparatus of FIG. 13 the length of the upper run can be foreshortened by mounting roll 21 closer to roll 22, namely, to the location at which the start of the second compression zone would be located if the apparatus were that of FIG. 11.

In the apparatus of FIG. 13 there is a roll 89 to the right of roll 21 (as viewed in FIG. 13) to continue the horizontal upper run of belt 16 beyond roll 21 and thereby minimize contact of belt 16 with belt 15 as the latter starts its movement around roll 21. This minimizes reverse flow of aqueous liquid from belt 15 through belt 16 to dewatered product. The belt 16 is trained around roll 89 and then around roll 70.

Referring to FIG. 1, which shows another embodiment of the apparatus of the invention, the apparatus is basically that shown in FIG. 1 1 except that it is not constructed to provide the first compression zone. In other words, rolls 24 and 25 and pan 43 of the apparatus of FIG. 11 are not present in the apparatus of FIG. 1. Thus belt 15 is not separated from belt 16 during their travel from roll 22 to the compression zone provided by sets of rolls 23 and sets of rolls 33. This partial dewatering zone can have the same length as the combined length of the initial partial dewatering zone, first compression zone and secondary partial dewatering zone of the apparatus of FIGS. 11 and 13. The actual length of the zone is, of course, dependent upon various factors including material to be dewatered, spaceage of belts, etc.

As an alternative to pipe 30 and manifold pipe 31 shown in FIGS. 1 1 and 13,-the apparatus of FIG. 1 has a trough 98 with a bottom outlet to a wide chute 99 to feed the sludge over a wide area of belt 16.

There are other differences between the apparatus of FIG. 1 and that of FIG. 11 and 13. The roll 50 instead of being located below roll 22 is located so that its top surface is at about the plane of the outer surface of belt 15 as it leaves roll 22. As a result, belt 16 starts a first part of the horizontal travel of its upper run without belt 15 being below in abutting relationship. Tracking devices located there can correct any wrinkling of belt 16 and can align belt 16 relative to belt 15.

In the apparatus of FIG. 1 rolls 75 and 61 are substantially to the right of roll so that belts 17 and 18 are shorter than in the apparatus of FIG. 11. In FIG. 11 they extend entirely over the upper run of belts 15 and 16. These longer belts 17 and 18 for the apparatus of FIG. 11 as compared with those in the apparatus of FIG. 1 provide a longer period of use before replacements. Furthermore, by this construction belts 16 and 18 can be made from sheets of their composite assembly of the same length.

Referring to FIG. 2, which shows belts 15 and 16, belt 15 is a composite assembly of elongated sheets 100 of porous cellular material having the wicking action and other properties stated earlier. The slabs or sheets 100 are between an elongated backing sheet 101 and a wide-mesh sheet generally indicated at 102. The ends of backing sheet 101 are secured to each other by a zipper (not shown) connected to both ends or other connecting means to form an endless belt. The wide-' mesh sheet 102 comprises longitudinal strands 103 and transverse strands 104 that are joined to each other at their intersections for a unitary construction. At these intersections or junctures sheet 102 is secured to backing sheet 101 by fasteners 105 (FIGS. 3 through 6). The distance between'adjacent longitudinal strands 103 and between adjacent transverse strands 104 is substantial, for example 3 to 4 inches.

The fasteners 105 are a type made by Dennison Manufacturing Co., Framingham, Mass, and have a construction generally that shown in US. Pat. No. 3,103,666 although the enlarged end of the fastener is flat rather than being bulbous button end as shown in that patent. Such fasteners are commercially available from that company with various lengths of shank. The flatness of that enlarged end minimizes the amount of material above the plane of the outer surface of sheet 100 so as to maximize the area of contact between sheet 100 and belt 16. The tool for securing the sheet 102 to backing sheet 101 with the shank of fastener 105 extending through sheet 100 is of the type disclosed in U.S. Pat. No. 3,103,666. Because of the wide spacing between adjacent strands 103 and between adjacent strands 104 only small areas of sheet 100 are compressed at the corners of the areas defined by the intersections of strands 103 and 104. Thus only a small amount of the total area of the outer surface of sheet 100 is changed to a level below the planarity of the rest of sheet 100. The bar 106 at one end of each fastener 105 abuts the side of sheet 101 that forms the inner surface of the composite assembly. This overall construction secures sheet 100 in an adequate manner to sheet 101 without the use of glue or other adhesive The other advantages of the use of sheet 102 secured to sheet 101 have been described above.

Referring to FIG. 7, in this alternative manner of securing strands 103 and 104 to backing sheet 101 at their intersections they are pressed down tightly to abut sheet 102 and heat welded to it. When backing sheet 101 and sheet 102 are made of suitable plastic, this can be done conveniently.

In the one alternative shown in the lefthand portion of FIG. 8 strands 103 and 104 at their intersection are connected by a pin 107 extendingthrough sheet 100. The ends of each pin 107 are welded to backing sheet 101 and sheet 102. In the other embodiment at the righthand portion of FIG. 8, sheet 102 is made with a number of depending pins 108 that are forced downwardly through sheet in making the composite assembly and their distal ends are heat sealed to backing sheet 101.

In FIG. 9 there is shown another alternative manner of securing sheet 102 to sheet 101. In this case a solid metal or plastic rivet 110 is used at the various spaced locations.

In FIG. 10 sheet 102, also at its intersections of strands 103 and 104, is also downwardly depressed and secured to backing sheet 101 by a metal or plastic staple 1 11.

Secured to the marginal edges of sheet 101 are plastic strips that have longitudinal beads at their distal longitudinal edges. (FIG. 2). Similarly, belt 16 has a pair of longitudinal strips 115 secured to an elongated different porous sheet 116. Thus sheet 116 and strips 115 secured to it constitute belt 16. Of course, the ends of sheet 116 and strips 115 of belt 16 are joined to provide endless belt 16.

Belt 17 is constructed like belt 15 as described above, but its sheet 100 is not required to be water absorbing by a wicking action. The belt 18 is constructed like belt 16.

For effective dewatering of sludge containing l'percent solids using the apparatus of the present invention a coagulant such as a commercially available polymer, sold under the trademark Magnifloc 52l-C, is mixed with the sludge before feeding it onto belt 16. For an initial determination of approximate coagulant dosage the following tests were performed. All free water was wrung from sheet 100 of belt 15 by operating the apparatus without the use of the wash sprays. A l-inch dam was then placed on sheet 116 of belt 16 at the initial partial dewatering zone with the apparatus not operating. The shape of the dam was rectangular and of a size to provide an area of 200 square inches. One liter of the sludge was applied to the dam area.

When the sludge mentioned below was used without any coagulant, it took in excess of 2 minutes for the sludge to change from a liquid state to a semi-solid state when sheet 100 was fine-pore cellulose sponge. Various amounts of the coagulant were added to quantities of this sludge and similarly fed to a dam area. With the high coagulant dosage there was almost immediate transformation of the sludge to a semisolid state. It happened almost as quickly as the dosed sludge was poured onto sheet 116. Using activated sludge containing 1% solids and obtained from the Metropolitan Sanitary District of Greater Chicago, it was found that the optimum economical coagulant dosage was the amount of coagulant that, when mixed with the sludge, provided a mixture that took, from the time it was fed to the darn area, approximately 20 seconds to change from the liquid state to the semisolid state.

For these tests to determine approximate coagulant dosage, the polymer was diluted to 1 percent (8.6 ml. of Magnifloc 52l-C/liter of water). In normal use the polymer at a 5 percent concentration is mixed with the sludge. It is indicated that a feed of 60 cc./min. of percent polymer with a sludge feed of gallons for such sludge is optimum.

Various tests have been performed with the apparatus basically disclosed in said second copending patent application but without the system shown in FIG. 1 of that application for drying the equivalent of belt 16. Further tests have been performed with the apparatus shown in FIG. 11 of the present application.

vant to improvement provided by the apparatus of FIG.

Using the previous apparatus, that lacks the compression by rolls 24 and 25 of the present apparatus, such ljpercent solids activated sludge admixed with coagulant is dewatered at its partial dewatering zone to a semisolid state containing 6 percent solids beforeit is compressed by the set of opposed rolls (equivalent to presentopposed rolls 23 and 33) during a series of compressions and expansions of the cellulose sponge belt. When using such admixture of sludge and polymer, it was found that the partially dewatered product on belt 16 of the apparatus of FIG. 11 of the present invention, using sheet 1 16 of cellulose sponge, was also semisolid with a solids content between 8 percent and 10 percent just prior to passage between rolls 23 and 33 of its second compression zone. This product had a higher viscosity than the 6 percent solids product mentioned above. The final product or sludge cake in both cases had a solids content between percent and 18 percent. However, the 8 percent solids product when compared with the 6 percent solids product established a substantial improvement of the dewatering prior to the additional dewateringby the compressions effected by rolls 23 and 33and the upper set of two belts.

The production of dewatered product having 8 percent solids instead of 6 percent solids saves about percent of the capacity of an anaerobic digester in which such dewatered material would be digested with primary sludge.

Activated sludge having 1 percent solids is a material that is not economically suitable to mix with primary sludge as a feed for such digester. The addition of a substantial amount of the activated sludge to primary sludge reduces substantially the overall solids content of the feed to 'the digester. This impairs the efficiency of the digester. To avoid this, it is conventional to treat activated sludge containing 1 percent solids by .a flotation process to obtain a product containing 4 percent to 5 percent solids. The availability of 6 percent solids product using the apparatus of said second copending application without its compression zone means a substantial saving of digester capacity from that required when using the 4 to '5 percent solids product from the flotation process. The 8 to 10 percent solids product when using the apparatus of FIG. 13 provides a further substantial saving of such capacity.

Although the solids content of sludge cake obtained from activated sludge with 1 percent solids using the apparatus of FIG. 11 is basically the same as the solids content of cake when using the apparatus of said second copending patent application, the overall quality of aqueous liquid removed from the fed sludge is substantially better. It has been concluded that this is because a substantial amount, e.g., about v percent, of the aqueous liquid tobe removed from the sludge is removed at the initial partial dewatering zone and then removed from the cellulose sponge sheet of belt 15 at the first compression zone. There is subsequent removal of aqueous liquid at the second partial dewatering zone to provide a product on belt 15 of higher solids content and higher viscosity. That product passes on belt 16 to the compression zone with belt 15 thatis now at a less than saturated condition. As a result, at

the compression zone there is less transfer of solids with aqueous liquid to sheet 100. From the experiments it was concluded that by the use of the apparatus of FIG. 11 to treat 1 percent activated sludge the aqueous liquid received by pan 43 can have a maximum solids contentof 30 parts per million (ppm). This aqueous liquid from the first compression zone is so low in solids content that it is a suitable material asa wash water at the various wash zones. The aqueous liquid collected by pan 43 would have .a-suspended solids contentof less than 100 ppm while the collected screen washings would have variable suspended solids content. A composite of these aqueous liquids would have a solids content of less than 200 ppm.

Tests for the apparatus of FIG. 11 with other materials than the 1% waste activated sludge were performed. When using aerobically digested sludge, the sludge cake contained between 20 percent and 25 percent solids. When using alum mud, the cake contained 35 percent to 40 percent solids.

In these tests with the apparatus of FIG. 11, the apparatus had a basic size of 5 feet wide, 20 feet long, and 6 feet high. The width of each of the four belts was 42 inches, while the effective loading width of belt 16 was 36 inches. The initial partial dewatering zone was about 6 feet long, as was the secondary partial dewatering zone. The second compression zone had a length that was only about one-sixth of the overall length of the three zones upstream of it. The second zone of these three zones, namely, the first compression zone, was, of course, shorter than the second compression zone. This is because there is only one compression between opposed rolls of belt 15 and the zone, as defined, includes the separating-lowering of belt 15 from belt 16, the passing of belt 15 between rolls 24 and 25 and returning it to abut belt 16 for the travel through the third zone and the second compression zone.

In view of the foregoing description of the apparatus of the present invention, many modifications will be obvious to one of ordinary skill in this art. The description has been presented solely for the purpose of illustration and not by way of limitation of the invention because the latter is limited only by the claims that follow.

We claim: I

1. An apparatus for removing aqueous liquid having a lower content of solids, if any, from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to

produce a material having a higher solids content, which comprises:

means at the second zone to compress said sheet of porous cellular material of said first belt by opa first endless belt including an elongated, compressisecond endless belt including an elongated different porous sheet, said different porous sheet being a fine-mesh sheet with pores extending through the sheet and of a size within a predetermined range for passage of said aqueous liquid of the continuous phase of said flowable material through said pores, from the outer surface to the inner surface of said different sheet, by a wicking action of said cellular sheet when it is in abutment with said inner surface of said different sheet, and for retention at the same time on said outer surface of said different porous sheet of a major portion of the suspended solids of said flowable material to obtain at least a partial removal of said aqueous posed forces acting on the outer and inner surfaces of that sheet of said first belt while spaced from ble and resilient sheet of a porous cellular material aid second belt and without applying said forces capable of absorbing said aqueous liquid by a to said spaced second belt; wicking action; means downstream of said third zone to compress means to support said belt at various positions to prosaid sheet of porous cellular material of said first vide a portion of the belt asan upper ru h 0ug belt by opposed forces acting on the outer and first, second and third zones through which said inner surfaces of that sheet of said first belt; belt is supported so that the outer surface of said means located at said second zone to collect aqueous elongated sheet is at a horizontal plane through liquid removed from said sheet of porous cellular said first and third zones and is below said horizonmaterial by said compression means at said second tal plane through said second zone and to provide 1 5 zone and moving downwardly from that sheet; and another portion of the belt as a lower run; means downstream of said third zone and adjacent means to move said endless belt through a path of said means to compress said sheet of porous cellutravel including said upper run at which said outer lar material downstream of said third zone to colsurface of said elongated sheet is at said horizontal lect aqueous liquid removed from and moving plane in said first and third zones; downwardly from that sheet.

2. The apparatus of claim 1 wherein said means at the second zone to compress said sheet of porous cellular material by opposed forces comprises a pair of opposed rolls between which said first endless belt passes, said opposed rolls being mounted below said second belt at the second zone.

3. The apparatus of claim 2 wherein said first endless belt is a composite assembly that includes, along with said sheet of porous cellular material:

an elongated coarse-mesh sheet as at least a part of a backing sheet for said sheet of porous cellular material on it; longitudinal strands of material, said strands being widely spaced from adjacent strands and on the liquid from said flowable material; side of said sheet of porous cellular material opmeans to support said second endless belt at various posite to the location of said backing sheet; and

positions to provide a portion of the belt as an means at widely spaced longitudinal intervals securupper run, at which the outer surface of said difing said strands to said coarse-mesh sheet with the ferent porous sheet faces upwardly, passing 40 sheet of porous cellular material thereby secured horizontally through said first, second and third to the backing sheet ina manner at spaced areas zones so that the inner surface of said different that the flatness of a major portion of the area of porous sheet is in abutment with the outer surface the outer surface of said sheet is retained. of said elongated sheet of porous cellular material 4. The apparatus of claim 3 wherein: for said wicking action at said first and third zones, said composite assembly includes transverse strands as initial and secondary partial dewatering zones, of material overlying said sheet of porous cellular and is spaced from the outer surface of said elonmaterial with said longitudinal strands, said transgated sheetof porous cellular material at said verse strands being widely spaced from adjacent second zone and to provide another portion of said strands and intersecting with said longitudinal second belt as a lower run; strands; and means to move said second belt through a path of said securing means are located at said intersections travel including said portion as said upper run and of the longitudinal strands and are spaced so that said another portion as said lower run, said moving at least 75 percent of the flatness of the outer surmeans moving said second belt so that its said face of said sheet of porous cellular material is upper run through the first and third zones is in the retained. same direction as the movement of said upper run 5- The apparatus of Claim 4 wherein: of said first belt; said sheet of porous cellular material is a sheet of means mounted above said upper run of said second fine-pore cellulose sponge;

belt to deliver said flowable material to said upsaid longitudinal strands and transverse strands are wardly facing outer surface of said different provided by a wide-mesh flexible sheet secured to porous sheet at a location adjacent the beginning said backing sheet by said securing means at locaof said initial partial dewatering zone; tions spaced to retain at least 90 percent of the means mounted downstream of said secondary parflatness of the outer surface of said sheet of porous tial dewatering zone to remove product of lower cellular material; and

liquid content and thus product of higher solids content from the outer surface of said different porous sheet of said second endless belt;

said different porous sheet of said second endless belt is at most only slightly absorbing of said liquid. 6. The apparatus of claim 5 wherein:

. 9 said wide-mesh flexible sheet is a polypropylene sheet with spacing between longitudinal strands and between transverse strands being sufficiently large so that the securing means are located at spaced areas such that at least 95 percent of the 5 flatness of the outer surface of the sheet of porous cellular material is retained after it is secured between the backing belt and the wide-mesh sheet by said securing means; and said different sheet is a polypropylene sheet substantially thinner than said sheet of porous cellular material and has a mesh size between about 50 microns and about 1,000 microns and with at least 25 percent open area. 7 5 7. The apparatus of claim 1 wherein: said support means for said first belt and said support means for said second belt at their upper runs includes a first set of rolls mounted downstream of said third zone at a second compression zone; said means downstream of said third zone to compress said sheet of porous cellular material of said first belt is at said second compression zone and includes in cooperation with said set of support rolls at that zone: a third endless belt including an elongated, compressible and resilient sheet of porous cellular material; means to support said third belt at various positio'ns to provide a lowermost portion of the belt that has its outer surface facing said first and second belts at said second compression zone; means to move said belt through a path of travel including moving said third belt at its said lowermost portion through said second compression zone in the same direction as said first and second belts; a fourth endless belt having the physical characteristics of said second belt; 40 means to support said fourth belt so that it-has at including moving said fourth belt at its said lowermost portion in portion an outer surface parallel to and facing the outer surface of said second belt at said second compression zone and at the same time has its inner surface facing the outer surface of said third belt at its said lowermost portion; means to move said fourth belt through a path of travel including moving said fourth belt at its said lowermost portion in the same direction as said first, second and third belts at said second compression zone; and a second set of rolls mounted above said first set of rolls for passage of said first through fourth belts between said first and second sets under compression.

8. The apparatus of claim 7 wherein said means at the second zone to compress said sheet of porous cellu- 6O lar material by opposed forces comprises a pair of opposed rolls between which said first endless belt passes, said opposed rolls being mounted below said second belt at the second zone.

9. The apparatus of claim 8 wherein said first endless belt is a composite assembly that includes, along with said sheet of porous cellular material:

an elongated coarse-mesh sheetas at least a part of a backing sheet for said sheet of porous cellular material on it;

longitudinal of material, said strands being widely spaced from adjacent strands and on the side of said sheet of porous cellular material opposite to the location of said backing sheet; and

means at widely spaced longitudinal intervals securing said strands to said coarse-mesh sheet with the sheet of porous cellular material thereby secured to the backing sheet in a manner at spaced areas that the flatness of a major portion of the area of the outer surface of said sheet is retained.

10. The apparatus of claim 9 wherein:

said sheet of porous cellular material is a sheet of fine-pore cellulose sponge;

said longitudinal strands are part of a wide-mesh flexible sheet having also widely spaced transverse strands intersecting said longitudinal strands;

said securing means are located at said intersections of the longitudinal strands and the transverse strands and are spaced so that at least percent of the flatness of the outer surface of said sheet of porous cellular material is retained; and

said different porous sheet of said second endless belt is at most only slightly absorbing of said liquid.

11. The apparatus of claim 10 wherein:

said wide-mesh flexible sheet is a polypropylene sheet with spacing between longitudinal strands and between transverse strands being sufficiently large so that the securing means are located at spaced areas such that at least percent of the flatness of the outer surface of the sheet of porous cellular material is retained after it is secured between the backing belt and the wide-mesh sheet by said securing means; and

said different sheet is a polypropylene sheet substantially thinner than said sheet of porous cellular material and has a mesh size between about 50 microns and about 1,000 microns and with at least 25 percent open area.

12. The apparatus of claim 1 wherein:

said compression means downstream of said third zone is mounted only at a location, upstream of which said first and second belts have passed through said third zone and been separated, so that only said first belt is compressed by that compression means; and

said means at the second zone to compress said sheet of porous cellular material by opposed forces comprises a pair of opposed rolls between which said first endless belt passes, said opposed rolls being mounted below said second belt at the second zone.

13. An apparatus for removing aqueous liquid having a lower content of solids, if any, from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to produce a material having a higher solids content, which comprises:

a first endless belt that is a composite assembly including: w an elongated, compressible and resilient sheet of a porous cellular material capable of absorbing said aqueous liquid by a wicking action;

an elongated coarse-mesh sheet as at least a part of a backing sheet for said sheet of porous cellular material on it;

longitudinal strands of material, said strands being widely spaced from adjacent strands and on the side of said sheet of porous cellular material opposite to the location of said backing sheet; and

means at widely spaced longitudinal intervals securing said strands to said coarse-mesh sheet with the sheet of porous cellular material thereby secured to the backing sheet in a manner at spaced areas such that the flatness of a major portion of the area of the outer surface of said sheet is retained;

means to support said belt at various positions to provide a portion of the belt as an upper run through a zone through which said belt is supported so that the outer surface of said elongated sheet of porous cellular. material is at a horizontal plane and to provide another portion of the belt as a lower run; means to move said endless belt through a path of travel including said upper run at which said outer surface of said elongated sheet of porous cellular material is at said horizontal plane at said zone;

a second endless belt including an elongated different porous sheet, said different porous sheet being a fine-mesh sheet with pores extending through the sheet and of a size within a predetermined range for passage of said aqueous liquid of the continuous phase of said flowable material through said pores, from the outer surface to the inner surface of said different sheet, by a wicking action of said cellular sheet when it is in abutment with said inner surface of said different sheet, and for retention at the same time on said outer surface of said different porous sheet of a major portion of the suspended solids of said flowable material to obtain at least a partial removal of said aqueous liquid from said flowable material;

means to support said second endless belt at various positions to provide a portion of the belt at an upper run, at which the outer surface of said different porous sheet faces upwardly, passing horizontally through said zone, as an elongated, partial dewatering zone, so that the inner surface of said different porous sheet is in abutment with the outer surface of said elongated sheet of porous cellular material and to provide another portion of said second belt as a lower run;

means to move said second belt through a path of travel including said portion as said upper run, said moving means moving said second belt so that its said upper run through said partial dewatering zone is in the same direction as the movement of said upper run of said first belt;

means mounted above said upper run of said second belt to deliver said flowable material to said upwardly facing outer surface of said different porous sheet at a location adjacent the beginning of said partial dewatering zone;

means mounted downstream of said partial dewatering zone to compress said sheet of porous cellular material of said first belt by opposed forces acting on the outer and inner surfaces of that sheet of said first belt; means located ad acent said means to compress said sheet of porous cellular material downstream of said partial dewatering zone to collect aqueous liquid removed from and moving downwardly from that sheet; and

means mounted downstream of said partial dewatering zone to remove product of lower liquid content and thus product of higher solids content from the outer surface of said different porous sheet of said second endless belt.

14. The apparatus of claim 13 wherein:

said support means for said first belt and said support means for said second belt at their upper runs includes a first set of rolls mounted downstream of said partial dewatering zone; and

said compression means being mounted at a zone through which the upper run of both belts abutting each other pass downstream of said partial dewatering zone, said compression means including a second set of rolls opposed to said first set and cooperating therewith for said compression.

15. The apparatus of claim 14 wherein:

said sheet of porous cellular material is a sheet of fine-pore cellulose sponge;

said longitudinal strands are part of a wide-mesh flexible sheet having also widely spaced transverse strands intersecting said longitudinal strands;

said securing means are located at said intersections of the longitudinal strands and the transverse strands and are spaced so that at least percent of the flatness of the outer surface of said sheet of porous cellular material is retained; and

said different porous sheet of said second endless belt is at most only slightly absorbing of said liquid.

16. The apparatus of claim 15 wherein:

said sheet of porous cellular material is a sheet of fine-pore cellulose sponge;

said longitudinal strands and transverse strands are provided by a wide-mesh flexible sheet secured to said backing sheet by said securing means at locations spaced to retain at least percent of the flatness of the outer surface of said sheet of porous cellular material; and

said different porous sheet of said second endless belt is at most only slightly absorbing of said liquid.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,699,881 Da ed October 24, 1972 Inventor-( Paul Levin, at. al.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected, as shown-below:

Column 19 lines 40 and 41, "including moving said fourth belt at its said lowermost portion in portion an outer surface" should read its lowermost portion an outer surface Column 20, line 4, v "longitudinal" should read longitudinal strands Signed and sealed this 1st day of May 19 73.

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

, ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents ORM 0-1050 (10-69) USCOMM'DC 6037G-P59 n U45. GOVERNMENT PRINTING OFFICE: I959 0'366-334, 

1. An apparatus for removing aqueous liquid having a lower content of solids, if any, from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to produce a material having a higher solids content, which comprises: a first endless belt including an elongated, compressible and resilient sheet of a porous cellular material capable of absorbing said aqueous liquid by a wicking action; means to support said belt at various positions to provide a portion of the belt as an upper run through first, second and third zones through which said belt is supported so that the outer surface of said elongated sheet is at a horizontal plane through said first and third zones and is below said horizontal plane through said second zone and to provide another portion of the belt as a lower run; means to move said endless belt through a path of travel including said upper run at which said outer surface of said elongated sheet is at said horizontal plane in said first and third zones; a second endless belt including an elongated different porous sheet, said different porous sheet being a fine-mesh sheet with pores extending through the sheet and of a size within a predetermined range for passage of said aqueous liquid of the continuous phase of said flowable material through said pores, from the outer surface to the inner surface of said different sheet, by a wicking action of said cellular sheet when it is in abutment with said inner surface of said different sheet, and for retention at the same time on said outer surface of said different porous sheet of a major portion of the suspended solids of said flowable material to obtain at least a partial removal of said aqueous liquid from said flowable material; means to support said second endless belt at various positions to provide a portion of the belt as an upper run, at which the outer surface of said different porous sheet faces upwardly, passing horizontally through said first, second and third zones so that the inner surface of said different porous sheet is in abutment with the outer surface of said elongated sheet of porous cellular material for said wicking action at said first and third zones, as initial and secondary partial dewatering zones, and is spaced from the outer surface of said elongated sheet of porous cellular material at said second zone and to provide another portion of said second belt as a lower run; means to move said second belt through a path of travel including said portion as said upper run and said another portion as said lower run, said moving means moving said second belt so that its said upper run through the first and third zones is in the same direction as the movement of said upper run of said first belt; means mounted above said upper run of said second belt to deliver said flowable material to said upwardly facing outer surface of said different porous sheet at a location adjacent the beginning of said initial partial dewatering zone; means mounted downstream of said secondary partial dewatering zone to remove product of lOwer liquid content and thus product of higher solids content from the outer surface of said different porous sheet of said second endless belt; means at the second zone to compress said sheet of porous cellular material of said first belt by opposed forces acting on the outer and inner surfaces of that sheet of said first belt while spaced from said second belt and without applying said forces to said spaced second belt; means downstream of said third zone to compress said sheet of porous cellular material of said first belt by opposed forces acting on the outer and inner surfaces of that sheet of said first belt; means located at said second zone to collect aqueous liquid removed from said sheet of porous cellular material by said compression means at said second zone and moving downwardly from that sheet; and means downstream of said third zone and adjacent said means to compress said sheet of porous cellular material downstream of said third zone to collect aqueous liquid removed from and moving downwardly from that sheet.
 2. The apparatus of claim 1 wherein said means at the second zone to compress said sheet of porous cellular material by opposed forces comprises a pair of opposed rolls between which said first endless belt passes, said opposed rolls being mounted below said second belt at the second zone.
 3. The apparatus of claim 2 wherein said first endless belt is a composite assembly that includes, along with said sheet of porous cellular material: an elongated coarse-mesh sheet as at least a part of a backing sheet for said sheet of porous cellular material on it; longitudinal strands of material, said strands being widely spaced from adjacent strands and on the side of said sheet of porous cellular material opposite to the location of said backing sheet; and means at widely spaced longitudinal intervals securing said strands to said coarse-mesh sheet with the sheet of porous cellular material thereby secured to the backing sheet in a manner at spaced areas that the flatness of a major portion of the area of the outer surface of said sheet is retained.
 4. The apparatus of claim 3 wherein: said composite assembly includes transverse strands of material overlying said sheet of porous cellular material with said longitudinal strands, said transverse strands being widely spaced from adjacent strands and intersecting with said longitudinal strands; and said securing means are located at said intersections of the longitudinal strands and are spaced so that at least 75 percent of the flatness of the outer surface of said sheet of porous cellular material is retained.
 5. The apparatus of claim 4 wherein: said sheet of porous cellular material is a sheet of fine-pore cellulose sponge; said longitudinal strands and transverse strands are provided by a wide-mesh flexible sheet secured to said backing sheet by said securing means at locations spaced to retain at least 90 percent of the flatness of the outer surface of said sheet of porous cellular material; and said different porous sheet of said second endless belt is at most only slightly absorbing of said liquid.
 6. The apparatus of claim 5 wherein: said wide-mesh flexible sheet is a polypropylene sheet with spacing between longitudinal strands and between transverse strands being sufficiently large so that the securing means are located at spaced areas such that at least 95 percent of the flatness of the outer surface of the sheet of porous cellular material is retained after it is secured between the backing belt and the wide-mesh sheet by said securing means; and said different sheet is a polypropylene sheet substantially thinner than said sheet of porous cellular material and has a mesh size between about 50 microns and about 1,000 microns and with at least 25 percent open area.
 7. The apparatus of claim 1 wherein: said support means for said first belt and said support means for said second belt aT their upper runs includes a first set of rolls mounted downstream of said third zone at a second compression zone; said means downstream of said third zone to compress said sheet of porous cellular material of said first belt is at said second compression zone and includes in cooperation with said set of support rolls at that zone: a third endless belt including an elongated, compressible and resilient sheet of porous cellular material; means to support said third belt at various positions to provide a lowermost portion of the belt that has its outer surface facing said first and second belts at said second compression zone; means to move said belt through a path of travel including moving said third belt at its said lowermost portion through said second compression zone in the same direction as said first and second belts; a fourth endless belt having the physical characteristics of said second belt; means to support said fourth belt so that it has at including moving said fourth belt at its said lowermost portion in portion an outer surface parallel to and facing the outer surface of said second belt at said second compression zone and at the same time has its inner surface facing the outer surface of said third belt at its said lowermost portion; means to move said fourth belt through a path of travel including moving said fourth belt at its said lowermost portion in the same direction as said first, second and third belts at said second compression zone; and a second set of rolls mounted above said first set of rolls for passage of said first through fourth belts between said first and second sets under compression.
 8. The apparatus of claim 7 wherein said means at the second zone to compress said sheet of porous cellular material by opposed forces comprises a pair of opposed rolls between which said first endless belt passes, said opposed rolls being mounted below said second belt at the second zone.
 9. The apparatus of claim 8 wherein said first endless belt is a composite assembly that includes, along with said sheet of porous cellular material: an elongated coarse-mesh sheet as at least a part of a backing sheet for said sheet of porous cellular material on it; longitudinal of material, said strands being widely spaced from adjacent strands and on the side of said sheet of porous cellular material opposite to the location of said backing sheet; and means at widely spaced longitudinal intervals securing said strands to said coarse-mesh sheet with the sheet of porous cellular material thereby secured to the backing sheet in a manner at spaced areas that the flatness of a major portion of the area of the outer surface of said sheet is retained.
 10. The apparatus of claim 9 wherein: said sheet of porous cellular material is a sheet of fine-pore cellulose sponge; said longitudinal strands are part of a wide-mesh flexible sheet having also widely spaced transverse strands intersecting said longitudinal strands; said securing means are located at said intersections of the longitudinal strands and the transverse strands and are spaced so that at least 75 percent of the flatness of the outer surface of said sheet of porous cellular material is retained; and said different porous sheet of said second endless belt is at most only slightly absorbing of said liquid.
 11. The apparatus of claim 10 wherein: said wide-mesh flexible sheet is a polypropylene sheet with spacing between longitudinal strands and between transverse strands being sufficiently large so that the securing means are located at spaced areas such that at least 95 percent of the flatness of the outer surface of the sheet of porous cellular material is retained after it is secured between the backing belt and the wide-mesh sheet by said securing means; and said different sheet is a polypropylene sheet substantially thinner than said sheet of porous cellular material and has a mesh size between about 50 microns and about 1,000 microns and with at least 25 percent open area.
 12. The apparatus of claim 1 wherein: said compression means downstream of said third zone is mounted only at a location, upstream of which said first and second belts have passed through said third zone and been separated, so that only said first belt is compressed by that compression means; and said means at the second zone to compress said sheet of porous cellular material by opposed forces comprises a pair of opposed rolls between which said first endless belt passes, said opposed rolls being mounted below said second belt at the second zone.
 13. An apparatus for removing aqueous liquid having a lower content of solids, if any, from a flowable material, containing aqueous liquid as a continuous phase and suspended solids as a discontinuous phase, to produce a material having a higher solids content, which comprises: a first endless belt that is a composite assembly including: an elongated, compressible and resilient sheet of a porous cellular material capable of absorbing said aqueous liquid by a wicking action; an elongated coarse-mesh sheet as at least a part of a backing sheet for said sheet of porous cellular material on it; longitudinal strands of material, said strands being widely spaced from adjacent strands and on the side of said sheet of porous cellular material opposite to the location of said backing sheet; and means at widely spaced longitudinal intervals securing said strands to said coarse-mesh sheet with the sheet of porous cellular material thereby secured to the backing sheet in a manner at spaced areas such that the flatness of a major portion of the area of the outer surface of said sheet is retained; means to support said belt at various positions to provide a portion of the belt as an upper run through a zone through which said belt is supported so that the outer surface of said elongated sheet of porous cellular material is at a horizontal plane and to provide another portion of the belt as a lower run; means to move said endless belt through a path of travel including said upper run at which said outer surface of said elongated sheet of porous cellular material is at said horizontal plane at said zone; a second endless belt including an elongated different porous sheet, said different porous sheet being a fine-mesh sheet with pores extending through the sheet and of a size within a predetermined range for passage of said aqueous liquid of the continuous phase of said flowable material through said pores, from the outer surface to the inner surface of said different sheet, by a wicking action of said cellular sheet when it is in abutment with said inner surface of said different sheet, and for retention at the same time on said outer surface of said different porous sheet of a major portion of the suspended solids of said flowable material to obtain at least a partial removal of said aqueous liquid from said flowable material; means to support said second endless belt at various positions to provide a portion of the belt at an upper run, at which the outer surface of said different porous sheet faces upwardly, passing horizontally through said zone, as an elongated, partial dewatering zone, so that the inner surface of said different porous sheet is in abutment with the outer surface of said elongated sheet of porous cellular material and to provide another portion of said second belt as a lower run; means to move said second belt through a path of travel including said portion as said upper run, said moving means moving said second belt so that its said upper run through said partial dewatering zone is in the same direction as the movement of said upper run of said first belt; means mounted above said upper run of said second belt to deliver said flowable material to said upwardly facing outer surface of said different porous sheet at a location adjacent the beginning of said partial dewaterinG zone; means mounted downstream of said partial dewatering zone to compress said sheet of porous cellular material of said first belt by opposed forces acting on the outer and inner surfaces of that sheet of said first belt; means located adjacent said means to compress said sheet of porous cellular material downstream of said partial dewatering zone to collect aqueous liquid removed from and moving downwardly from that sheet; and means mounted downstream of said partial dewatering zone to remove product of lower liquid content and thus product of higher solids content from the outer surface of said different porous sheet of said second endless belt.
 14. The apparatus of claim 13 wherein: said support means for said first belt and said support means for said second belt at their upper runs includes a first set of rolls mounted downstream of said partial dewatering zone; and said compression means being mounted at a zone through which the upper run of both belts abutting each other pass downstream of said partial dewatering zone, said compression means including a second set of rolls opposed to said first set and cooperating therewith for said compression.
 15. The apparatus of claim 14 wherein: said sheet of porous cellular material is a sheet of fine-pore cellulose sponge; said longitudinal strands are part of a wide-mesh flexible sheet having also widely spaced transverse strands intersecting said longitudinal strands; said securing means are located at said intersections of the longitudinal strands and the transverse strands and are spaced so that at least 75 percent of the flatness of the outer surface of said sheet of porous cellular material is retained; and said different porous sheet of said second endless belt is at most only slightly absorbing of said liquid.
 16. The apparatus of claim 15 wherein: said sheet of porous cellular material is a sheet of fine-pore cellulose sponge; said longitudinal strands and transverse strands are provided by a wide-mesh flexible sheet secured to said backing sheet by said securing means at locations spaced to retain at least 90 percent of the flatness of the outer surface of said sheet of porous cellular material; and said different porous sheet of said second endless belt is at most only slightly absorbing of said liquid. 